Worldwide, refiners have increased the amount of processing heavier crudes in their crude basket due to availability at cheaper cost. These crudes contain higher proportion of heavier fractions containing higher quantity of large amounts of aromatics such as asphatlenes and resins and impurities such as sulfur, nitrogen, nickel, vanadium, sodium. The heavier fractions cannot be economically distilled or catalytically cracked due to high coke make and catalyst deactivation by ash and metals. The heavier fractions are normally processed in conventional Delayed Coking process to convert low value heavy residuum to valuable distillates. As a result, the generation of fuel oil is much higher and available in surplus quantity. In most cases, fuel oil is economically the least desirable product for the refiner, upgrading the fuel oil to further valuable middle distillates and gaseous products in the conventional Delayed Coking process will certainly improve the refinery margins.
U.S. Pat. No. 3,619,413 describes a delayed coking process in which small amounts of hydrogen halide or hydrocarbyl halides are added to the heated feed to the coke drums. The addition of such halides is alleged to make the volatile content of the coke more uniform without affecting the distillate yield adversely.
U.S. Pat. No. 4,169,041 describes a fluid hydrocoking process in which metallic hydrogenation catalysts, particularly molybdenum, chromium, and vanadium are added to the fluid coking feedstock. The addition of such metals is reported to increase distillate yield and reduce coke yield. U.S. Pat. Nos. 2,888,393 and 2,888,395 also teach the use of hydrogen and hydrogen plus catalyst, respectively, in fluid coking.
US Patent US 2010/0170827A1 describes a process for improving yield of desired products from Delayed coking process by supplying a catalyst material in the top section of the drum, which falls into the liquid pool inside the coke drum, which during its downward motion, contacts the product vapors and catalytically cracks the same to lighter material. But, here the major disadvantage is that the whole of the catalyst material is settled inside the liquid pool inside the coke drum and gets deposited in the solid petroleum coke formed during the thermal cracking of feedstock. This necessarily increases the ‘ash content’ of the coke that is produced from the process, making the coke out of specifications of the coke customers.
The control over vapor-catalyst contact time is limited by the gravity fall of the catalyst particles through the drum and also the contact time of catalyst particles with the product vapors will vary throughout the coke drum filling cycle, since the height of liquid pool increases throughout the cycle with increased quantities of feed is supplied to the drum.
Therefore, it is desirable to have a process which overcomes the above stated drawbacks in the prior art to facilitate the refiner to effectively utilize a catalyst for improving the yield pattern from the delayed coking process. The present subject matter attempts to provide an alternate process and apparatus to address these issues.